The permeability of most fabrics and fabric based articles to fluid passage is set during manufacturing. Parameters such as the materials from which the fabric is made, the weave density and pattern, and the general structure such as holes formed in the fabric, control its permeability. However certain articles may benefit from the ability to dynamically control such permeability. By way of example, parachutes, sails, filters, and aircrafts may all benefit from the ability to control the rate at which fluid passes therethrough.
Attempts at providing variable permeability in fabrics have been made for various purposes. By way of example, U.S. Pat. No. 3,222,016 discloses a variable permeability fabric for a parachute. U.S. Pat. No. 5,115,582 discloses a spiral fabric papermaker belt having adjustable permeability. U.S. Pat. No. 7,820,571 discloses a fabric exhibiting reversibly changeable air permeability responsive to humidity. In US 2008/0254263, Yausi et al. disclose a composite fabric material exhibiting three dimensional structural change upon water absorption.
In these specifications the terms variable permeability and controlled permeability, and the varied inflictions of those terms, are also used interchangeably. A fabric based article should be construed to mean an article which is primarily made of fabric, regardless if other materials are incorporated in the article or if the fabric article is incorporated within another article, and modifies the permeability of the article in which it is incorporated.
Methods of controlling fabric permeability are generally broadly divided between two main categories, referred to herein as geometric permeability, and weave permeability. Controlled weave permeability is determined by the weave of the fabric, and its finish. Weave permeability modifies either the pore size between adjacent strands, or changes the shape or geometry of the weave of the fabric itself. In contrast, variable geometric permeability involves changing the geometry of a fabric based article as a whole. Therefore changes to the general shape, or more commonly, opening or by closing of holes, slots and other voids of various shapes within the fabric article, change the permeability of the article as a whole. In geometric permeability the openings are generally significantly larger than the distance between adjacent strands of the fabric. Thus, while variable geometric permeability relates to the permeability of the fabric based article, variable weave permeability relates to changes in the permeability of the fabric itself, regardless of the article in which it is used.
Changes in geometrical permeability may effect the weave permeability, and vice versa. Modifying the permeability of the fabric itself effects the permeability of the fabric based article as a whole, but the weave based variable permeability deals firstly with the permeability of the fabric. Similarly, in many instances, deforming the fabric to open or close a void may also cause change in the fabric weave. However the effects of those weave changes are minor relative to the change in permeability caused by opening or closing of voids, or otherwise changing the geometry of the fabric. Clearly, these specifications and the claims should be construed to extend to combinations of such variable permeability types.
Shape Memory Alloys (commonly known as SMA) are well known in the art. SMA are materials that tend to have a phase change which is induced by environmental factors to which the material is exposed, such as temperature, electromagnetic fields, electric currents, and the like. An object made of SMA material is initially formed into a ‘parent shape’ by machining, heat treatment and other metalwork techniques. The object may then be manipulated, deformed, bent, stretched and the like, and would generally maintain the shape to which it is manipulated. However, once exposed to specific known conditions, the material goes through the phase change, and resumes the ‘parent shape’, in a process known as ‘shape memory transformation’. Certain SMAs are capable of ‘memorizing’ two shapes, one for high temperature and the other for low temperature, or for two states of the known conditions. A common SMA material is known in its commercial name NITINOL (Nickel Titanium Naval ordinance Laboratory), however the invention is not limited to use of any specific material.
Certain medical applications of SMA are directed at forming a medical device such as stents, filters, and the like, which are either made of SMA materials, or are based on its operation. Generally those devices are based on forming a structure comprising SMA material and shaping it into substantially a parent shape. The material is then deformed, and placed in a body cavity such as a blood vessel, intestinal or urinary tract, and the like. Placement occurs by different means, but generally a catheter is a common tool used to insert the device into its position in the body, and the SMA allows a relatively large structure, to be positioned by a much smaller catheter. Examples of such applications are described, by way of example, in US2007/0135834 to Clubb et al., U.S. Pat. No. 7,367,985 to Mazzocchi et al., and in US2008/0228028 to Carlsom et al. Certain devices utilize the body temperature to transition the SMA base object to a desired shape, once inside a desired location in a human body.
U.S. Pat. No. 6,164,339 and U.S. Pat. No. 6,192,994, both to Greenhalgh, disclose a method of manufacturing a woven textile having a structural member integrally woven therein. The structural member comprises a wire which is trained to undergo a shape memory transformation. The straight wire is inserted into the fabric during manufacturing, and is transformed back to an undulating shape thereafter. Greenlhlag is directed to creating a combined stent/graft structure for repair of a body tube in a living body. It is noted that the above examples are designed for forming a device, and shaping it to a temporary shape utilizing various combinations of temperature, pressure, and the like, and then allowing it to get back to its original shape once deployed. That action is expected to take place only once in the useful life of the device. The above devices do not take advantage of the SMA ability to repeatedly move from one state to another responsive to repeated heating and cooling thereof.
In US 2004/0183283, Buckman et al. disclose a personal air bag inflation device which optionally utilizes garments fabricated from fibers that are highly flexible in their unactivated state, such as Nitinol. Following activation, these fibers become more rigid and provide additional impact, penetration, and skid protection. The nitinol shape-memory elements may be comprised of nanofabricated or micromachined into the cloth of the garment. Activation of the microscopic nitinol shape-memory elements by applying electricity to the elements, causes them to change shape to stiffen the fabric or cloth of the garment.
SMA actuators are known, whereby electrical current is passed in a wire made of SMA material. The resulting temperature change causes the wire to contract or expand proportionally to the amount of current. Such wires act as fast, light weight, and relatively high powered actuators. In most cases, the actuators may be continuously adjusted between a ‘relaxed’ state and a ‘fully activated’ state Control of fabric permeability while fabric based articles are being used, provides special advantages that are oftentimes specific to the application at hand. Thus, by way of example changing the air permeability of a fabric used in a parachute offers better control of the opening speed and shock, the decent rate, and landing speed of the parachute, as well as controlling oscillations, possibly changing direction of the descent, and the like. Providing a boat sail with controlled air permeability allows optimizing the sail shape to current conditions such as wind strength and direction, allowing spilling of air from the sail at desired areas, may act as a substitute to reefing the sail, and the like. Filters made by utilizing variable permeability offer the ability of changing the particle size which they filter, and optionally offer a cleaning method of the filter by changing the pore size at selected times.
There is therefore a clear and heretofore unanswered need for materials and methods to dynamically change the fluid permeability of a fabric in a controlled manner, as well as for articles utilizing such materials and methods.